PIRATES were kept away from the British cruise ship Spirit of Adventure by a loud sonic boom device deployed to deafen them, sources revealed last night.

More than 350 passengers, most British, were ordered to stay inside the ship as Somali pirates approached in the Indian Ocean last week.

But as the cruise liner was being “buzzed” by a speedboat during the night-time attack, its Australian captain, Frank Allica, ordered the deployment of the long range acoustic device, known as LRAD, which can cause permanent deafness at 300 feet.

The device emits a loud boom that can be effective from as far away as 800 feet, though it cannot be heard by those standing behind it. Passengers aboard the Spirit had already been grouped in the barricaded dining room and resumed their black-tie dinner as soon as the danger had passed.

The Spirit of Adventure’s operator, Saga, would not divulge what deterrents were used, but sources have told the Sunday Express that measures also included throwing tangling cables designed to snarl the pirates’ speedboat propellers .

Passengers on the Spirit of Adventure disembarked safely in Tanzania last night, as they continued their £2,000-a-head cruise unfazed.

Insurance premiums for passenger liners passing through the pirate-infested waters around the Gulf of Aden have trebled in the last two years.

“We need much more robust maritime laws,” said Sean Woollerson, of insurance giant JLT. “Most people don’t realise that United Nation maritime law means that, even if a pirate vessel is inspected and a whole stash of guns and rope ladders discovered, the pirates themselves must be released unless they are actually caught in the act. It’s extremely frustrating.”